Heavy duty trucks such as large, tandem axle trucks commonly employ leaf spring suspension assemblies. A leaf spring suspension may include a plurality of stacked leaf springs. The springs are secured at their centers to the truck frame by means of a center post at a location between the axles. The springs extend from their centers to the respective axles in cantilever fashion. Typically, a pair of leaf spring suspension assemblies are used for each pair of axles with one leaf spring suspension assembly being positioned on either side of the truck. The ends of the springs may be connected to the axles by bearings. The bearing may include an elastomeric member configured and positioned to allow relative movement between the spring and the associated axle to prevent damage to the spring or undue limitation of the axle travel. Examples of such elastomer bearings may be found in U.S. Pat. Nos. 5,676,356, 5,020,824, 4,322,061, 3,099,459, 2,929,618, and 2,831,674.
In a leaf spring suspension assembly as described above, the wheels, axles and springs may undergo a wide range and variety of deflections and combinations of deflections in use. For example, when the truck is traveling over rough terrain or curbs, the wheels and, thus, the adjacent axles, may move independently and through large degrees of displacement. If a wheel on one end of an axle is displaced upwardly while the wheel on the opposite end of the axle is displaced downwardly, the axle will pivot and thereby induce a conical torsional load which tends to twist the leaf springs. Moreover, if one wheel is displaced upwardly and the adjacent wheel (on the adjacent axle) is displaced downwardly, the respective axles will pivot in opposite directions and thereby induce a torsional load which tends to conically deflect the respective ends of the leaf springs in opposite directions. As a wheel travels vertically upwardly or downwardly and flexes the leaf spring assembly beyond its neutral position, the vertical angle between the leaf spring end and the axle is changed, thereby inducing a localized load on the end of the spring which may tend to bend the leaf springs. One end of the wheel may also be displaced laterally so that the wheel is rotated about a vertical axis, again inducing a torsional load on the spring.
It is important that such deflections and combinations of deflections not result in damage to the leaf spring assembly. It is also important that the leaf spring suspension and the components thereof be durable and not negatively affect the handling of the vehicle.
One problem encountered with multiple or tandem axle vehicles is that a misalignment of the axles may cause significant wear damage to the tires and other components. Moreover, misalignment may degrade the handling of the vehicle. Typically, the relative alignment of the axles is established at the factory during manufacture of the truck. It is not uncommon for the axles to become misaligned thereafter as a result of impacts in use or improper replacement or repair of components of the suspension and drive train.
Thus, there exists a need for a means for accommodating the various pivotal loads applied between an axle and a leaf spring assembly. Such means should not negatively affect the operability or handling of the vehicle. Such means should be durable. Moreover, there is a need for means for conveniently and effectively adjusting alignment between axles of a tandem axle vehicle, particularly of the type employing a leaf spring suspension.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.